and pathways of penetration, uptake, and migration of nanoparticles in wheat plants.
Wild and Jones (2009) used two-photon excitation microscopy to observe multiwalled carbon nanotubes piercing the cell wall of wheat roots and reaching the
cytoplasm. After root uptake and penetration of the epidermal cells of nanomaterials,
further transport requires circulation across the root and to the xylem. Nanoparticles
are transported through cell wall pores via apoplastic or symplastic pathway through
plasmodesmata and channels that connect adjacent cells (Fig. 5.1). Magnetic carboncoated nanoparticles of 5–50 nanometers were absorbed by the roots and then
translocated to the xylem vessels up to the leaves via trichomes. However, nanoparticle absorption by wheat roots and translocation of nanoparticles in stems and leaves
is largely influenced by physicochemical features of nanoparticle, growth stage of
plant, and growth medium (Cifuentes et al. 2010). Taran et al. (2017) used nonionic
colloidal solutions of nanoparticles (iron, zinc, and manganese) in winter wheat to
test concentration in seedlings either arising from pretreated seeds or sprayed with
nanoparticles after growth. The outcome of the study provided evidence for the
absorption and translocation of manganese and zinc from the foliar epidermis in
wheat seedlings. Du et al. (2011) treated wheat plants with titanium dioxide
nanoparticles and zinc oxide nanoparticles of 20–100 nanometers in size under
field conditions using outdoor lysimeters. Titanium dioxide nanoparticles either
agglomerated or adhered to the cell walls of the root periderm, and particles of
50 Æ 10 nanometers penetrated the primary epidermis roots and the cortex via
apoplast up into cell vacuoles; however, zinc oxide nanoparticles seemed to dissolve
and then penetrate the cells in the form of zinc ions. Root uptake of titanium dioxide
nanoparticles appears to be size selective (Tripathi et al. 2017). Larue et al. (2012a)
postulated that threshold diameters for movement of titanium dioxide nanoparticles
through root epidermis of wheat plants should be smaller than 140 nm; thresholds for
transferring through parenchyma are 36 nm or less; and for passing through the
Casparian band, particle diameters should be smaller than 36 nm. Titanium dioxide
nanoparticles smaller than 36 nm could be transported to the stele via two routes:
(i) direct penetration of Casparian band and (ii) through plasmodesmata (Larue et al.
2012b). Additionally, titanium dioxide nanoparticles may enter plant cells through
endocytosis as nanoparticles have been shown to activate membrane receptors and
induce endocytosis (Iversen et al. 2011). Recently, Pradas del Real et al. (2017)
investigated the uptake and transfer pathways of silver nanoparticles and sulfidized
silver nanoparticles in wheat and the changes in speciation. The results showed that
the sulfidation of silver nanoparticles is not a perfect antidote to toxicity and
sulfidized silver nanoparticles are not as stable as expected when exposed to plant
roots. Moreover, the rhizospheric activity of wheat seedlings partly dissolves silver
sulfide causing some impacts on crop quality and yield and more on ecological
services. Further, the study illustrated the complexity of the toxicity pattern for
plants exposed to silver nanoparticles, where both apoplastic and symplastic transfer
of silver in monovalent form in wheat plants (Pradas del Real et al. 2017). Similarly,
the effect of citrate-coated iron oxide nanoparticles on hydroponically grown wheat
plants was studied by Iannone et al. (2016). The authors mentioned the deposition of
5 Nanotechnology in Wheat Production and Protection
169
Wild and Jones (2009) used two-photon excitation microscopy to observe multiwalled carbon nanotubes piercing the cell wall of wheat roots and reaching the
cytoplasm. After root uptake and penetration of the epidermal cells of nanomaterials,
further transport requires circulation across the root and to the xylem. Nanoparticles
are transported through cell wall pores via apoplastic or symplastic pathway through
plasmodesmata and channels that connect adjacent cells (Fig. 5.1). Magnetic carboncoated nanoparticles of 5–50 nanometers were absorbed by the roots and then
translocated to the xylem vessels up to the leaves via trichomes. However, nanoparticle absorption by wheat roots and translocation of nanoparticles in stems and leaves
is largely influenced by physicochemical features of nanoparticle, growth stage of
plant, and growth medium (Cifuentes et al. 2010). Taran et al. (2017) used nonionic
colloidal solutions of nanoparticles (iron, zinc, and manganese) in winter wheat to
test concentration in seedlings either arising from pretreated seeds or sprayed with
nanoparticles after growth. The outcome of the study provided evidence for the
absorption and translocation of manganese and zinc from the foliar epidermis in
wheat seedlings. Du et al. (2011) treated wheat plants with titanium dioxide
nanoparticles and zinc oxide nanoparticles of 20–100 nanometers in size under
field conditions using outdoor lysimeters. Titanium dioxide nanoparticles either
agglomerated or adhered to the cell walls of the root periderm, and particles of
50 Æ 10 nanometers penetrated the primary epidermis roots and the cortex via
apoplast up into cell vacuoles; however, zinc oxide nanoparticles seemed to dissolve
and then penetrate the cells in the form of zinc ions. Root uptake of titanium dioxide
nanoparticles appears to be size selective (Tripathi et al. 2017). Larue et al. (2012a)
postulated that threshold diameters for movement of titanium dioxide nanoparticles
through root epidermis of wheat plants should be smaller than 140 nm; thresholds for
transferring through parenchyma are 36 nm or less; and for passing through the
Casparian band, particle diameters should be smaller than 36 nm. Titanium dioxide
nanoparticles smaller than 36 nm could be transported to the stele via two routes:
(i) direct penetration of Casparian band and (ii) through plasmodesmata (Larue et al.
2012b). Additionally, titanium dioxide nanoparticles may enter plant cells through
endocytosis as nanoparticles have been shown to activate membrane receptors and
induce endocytosis (Iversen et al. 2011). Recently, Pradas del Real et al. (2017)
investigated the uptake and transfer pathways of silver nanoparticles and sulfidized
silver nanoparticles in wheat and the changes in speciation. The results showed that
the sulfidation of silver nanoparticles is not a perfect antidote to toxicity and
sulfidized silver nanoparticles are not as stable as expected when exposed to plant
roots. Moreover, the rhizospheric activity of wheat seedlings partly dissolves silver
sulfide causing some impacts on crop quality and yield and more on ecological
services. Further, the study illustrated the complexity of the toxicity pattern for
plants exposed to silver nanoparticles, where both apoplastic and symplastic transfer
of silver in monovalent form in wheat plants (Pradas del Real et al. 2017). Similarly,
the effect of citrate-coated iron oxide nanoparticles on hydroponically grown wheat
plants was studied by Iannone et al. (2016). The authors mentioned the deposition of
5 Nanotechnology in Wheat Production and Protection
169